The invention relates to a method of installing liners in steel casings in order to increase the internal pressure containment capability of the flowline.
It is presently known to construct flowlines by installing thermoplastic liners in steel casings, or pipelines, in order to protect the casing from fluids being carried in the liner. Typically, the liner has a smaller outer diameter than the inside diameter of the casing, and the annular space between the two is filled with a solid material to protect the liner from any corrosion of the casing and to transfer stress through the solid material to the outside casing. One such method is described in U.S. Pat. No. 3,662,045, filed by the present inventor, which describes a method of installing a liner in a field flowline.
Over the years, improvements have been directed at changes in grouting techniques in order to protect the integrity of the liner, as well as methods of bonding the liner to the grout. More recently, the liners used have been inflatable or expandable into a cylindrical configuration after insertion into the pipeline. The methods used must contend with the fact that stress relaxation of the liner (creep) can reduce the internal pressure containment of the system. At any rate, the liners presently used do not contribute to the internal pressure bearing capability of the flowline because of the high elasticity of the liner relative to the pipe (casing) and grout.
It would be desirable to build a flowline with a liner that actually increases the internal pressure containment capability of a flowline.